Composition comprising a rubber, lignin and polyisocyanate and method of preparing same



Umed Sim P wmC COMPOSITION COMBRISING A,RUBBER, LIGNIN AND 'POLYISOCYANATE AND METHOD OF PREPARING SAME v George S. Mills, Pompton'allaingand Henry EJ-Iaxo, Jr., Bloomfield, 1N.'J., .assignors to .United'States. Rubber fompany, New York,,N.Y.,, a. ,corppration,of New ersey No Drawing. Application April 17, 1956 Serial No. 578,568

18 Claims. cram-.115

lignin solids, which couldthereafter be processed much like ordinary rubber stocks. Such methods are disclosed in U.S. Patent 2,608,537 issued to Pollak on August 26, 1952, andtin an article by Keilen and Pollak entitled Ligninfor Reinforcing Rubber, Ind. Eng. Chem., 39} 480-483 '(April 1947). ventionally prepared the lignin-reinforced rubber products are frequently boardy and poor in abrasion resistance.

We have .nowvdis'covered that if the lignincontaining rubber stock is..treated with'an organic polyisocyanate prior to vulcanization, there is obtained after cure a product having markedly improved physical properties, especially higher abrasion resistance and reduced torsional hysteresis.

According to theinvention the lignin-containing rubber stock or masterbatch, in ,the. uncured state, is ,mixed intimately with an organic ,polyisocyanate. The stock so prepared may' contain previously added ,additional compounding ingredients; or such compoundingingredients, including suitable conventional curatives and the like, may ,beadded subsequent to the treatment with the polyisocyanate. The thus-treated, lignin-containing, compounded rubber stock is thereafter shaped and cured by .heat in any desired form-in accordance with the usual practices in molding or otherwise fabricating rubber articles.

The rubber latex used in the present invention maybe natural rubber latex, or a conjugated diene polymer synthetic rubber latex, or mixtures of any of .the same. Such conjugated diene polymersynthetic rubber latexmay be an aqueous emulsion polymerizate of a 1,3-butadiene,

such as LB-butadiene, Z-methyI-butadiene (isoprene),

piperylene, 2,3-dimethyl butadiene, or a mixture of such 1,3-butadienes. Theconjugated diene polymer synthetic rubber latex may alsobe'an aqueous emulsion polymerizate of a mixture of one or more of such l,3-butadienes with one or more other polymerizable compounds which are capable of forming rubbery copolymers with 1,3- butadiene, for example, up to 70% of such mixture of one or. more compounds which contain a single CH =C group where at least one. of the disconnected valences is However, as con- Z,9ilb,7l8 Patentedsept. 29, 1959 ICC attachedto an electro-negative group, that is, a group which substantially increases the electrical dissymmetry or polar character of the molecule. Examples of such monoolefinescontaining a terminal methylene group which are copolymerizable with l,3-;butadie nes are styrene, vinyl toluene, vinyl naphthalene, alpha methyl styrene, parachloro styrene, dichlorostyrene, alpha methyl dichloro styrene, methyl acryl'ate, ethyl acrylate, methylmethacrylate, acrylonitrile,; methacrylonitrile, vinyl pyridines such as 2-v'inyl pyridine, and-alkyl vinyl pyridines such as Z-methyl-S-vinyl pyridine.

The lignin used in the present invention is preferably the lignin commonly recovered by precipitation from its soluble sodium salt in the black liquor in the kraft sulfate process of wood pulping by acidification of the waste liquor. Ligninis readily soluble in-aqueous alkali (e.g. alkali-metal hydroxide or ammonium hydroxide solution) :to formialkaline lignate solution in which form it is mixed .withthe rubber latex. Modified lignins 'that are soluble in .alkalies andiinsoluble in acids may'also be used in the present invention. Examples of such modified lignins arev oxidized-lignin, slightly chlorinated lignin, slightly nitrated lignin, slightly sulfonated lignin (made either by partially desulfonating thesulfonated lignin made by vthe sulfite pulp process or -by partially sulfonating alkali ligninmade by the sulfate'pulp process); such modified ligninsv are equivalent .to the lignin made by acidification .of-waste liquorjin the sulfate pulp process in the present invention.

In preparing the lignin-rubber masterbatch according 'tol e p esent invention, the lignin in the form of an alkaline aqueous solutionis admixed. with the latex, as

.shownfor example in the Pollakapatent and the Keilen et al. article previously referred to. The rubber and lignin thus become intimately mixed in ;the aqueous 'medium from whichthe solids maybe recovered by ,eo-coagulation in anysuitable manner, .such as byI spray drying or by coprecipitating, e.g. by means of ,a dilute acid suchas formic or sulfuricv acid. The -r esultin g co-coagulated lignin and rubber rnasterbatch is :then washed and dried, andused'directly in the practi ce of the present invention. The ratio-of lignin to rubber in thelignin-rubber masterbatch usually ranges from 25; to 100, parts per IOOparts of rubber. If desired, anysuitableadditional compounding ingredient may be milled into or otherwise incorp te in the mixture at yr pp opr et st geincludin carbon-blacker other fillers, the usual vulcanizing agents,

accelerators, antioxidants, etc. Compounding ingredients added -before the polyisocyanate must of course,.-be unreactive with'thepolyisocyanate. If desired, the rubber a part generally one-half or more, of-thetotal rubber hasbeen co-coagulatedwith the lignin, additional rubber may. e. added to the master-batch on the millbefore addingthe polyisocyanate and still retain the advantages of our, invention.

v{I'heprganic p'olyisocyanateused to treat the masterbatch or unvulcanized lignin-rubber stock in accordance .with ,thetinvention may ,;-be, any known t polyisocyanate,

such as a diisocyanate or a triisocyanate. Examples are polymethylene diisocyanates such as ethylene ,(diisocyanate, hexamethylene diisocyanate and tetramethylene Among the triisocyanates may be mentioned those having isocyanate groups attached to a trivalent hydrocarbon radical, whether an aliphatic, aromatic, or aliphaticaromatic radical as in butane-1,2,2-triisocyanate, benzene- 1,3,5 triisocyanate, diphenyl 2,4,4 triisocyanate, phenyl-4,6,4'-triisocyanate, toluene 2,4,6 triisocyanate, ethyl benzene-2,4,6-triisocyanate, and triphenylmethane 4,4,4"-triisocyanate. Triisocyanates derived from corresponding substituted trivalent hydrocarbon radicals, such as monochlorobenzene-2,4,6-triisocyanate may also be used. 1

For purposes of the invention, a small amount of the polyisocyanate is simply milled into or otherwise suitably uniformly incorporated in the solid lignin-rubber mixture. cold mill or on a heated mill, and the mixing need not be any more prolonged than is necessary to produce a homogeneous stock. The polyisocyanate is highly effective in producing the desired improvements, and as little in 100 parts of rubber is sufiicient to produce noticeable improvement. We generally prefer to use somewhat more polyisocyanate than this, say 1- or 2 parts, and increasing benefits may be noted with increasing quantities This mixing maybe carried out either on a -as about one-half of one part by weight of polyisocyanatc of polyisocyanate, up to about 8 or 10 parts, or even i 2 performed both before and after adding the polyisocyanate. Theheat treatment is typically accomplished by heating the mixture at an elevated temperature for a suitable period of time, say for a period of from 5 minutes to 1 hour with mastication, or from 2 to 10 hours statically, at a temperature of from 200 F. to 350 F. oreven higher, provided care is taken not to heat the mixture so long or at such a high temperature as to cause thermal injury. (The shorter times of treatment are most suitably employed with the higher treating temperatures, and conversely, longer treating times are appropriately employed with the lower temperatures mentioned.) To avoid pre-vulcanization such heat treatment will of course be carried out before the vulcanizing agent is added to the compound. Particular care should be taken to avoid too much heating of the polyisocyanate treated lignin-rubber mix, as it is subject to scorching. Best results are achieved by hot mastication or static heating of the ligninrubber masterbatch prior to the addition of the polyisocyanate, followed by further mastication on a cold mill after completing the addition of polyisocyanate.

Good results have been obtained by masticating the phenolic and hydroxyl groups) as well as with the rubber molecule. 7

Among the improved desirable properties obtained by the invention are:

(1) Improved abrasion resistance of 40% to 100% in the case of polyisocyanate treated GR-S/lignin and butadiene-methyl methacrylate/lignin coprecipitates as shown by laboratory and road tests, and to a lesser but substantial extent in the case of vinyl pyridine-butadiene/lignin mixes, so treated.

(2) Lowered torsional hysteresis as determined by decrements of observed amplitudes of successive oscillations of a torsional pendulum as explained in Gerke et al., U.S.P. 2,118,601.

(3) Higher modulus by A.S.T.M. methods.

(4) Reduced Shore A hardness for comparable moduli.

(5) Higher percent bound rubber and reduced swelling indices, indicating greater cross-linking. The expression bound rubber refers to a value that may be calculated from the gel content; thus:

Bound rubber percent gel.-percent known insoluble matter percent rubber It is believed that increased bound rubber values are indicative of an increased degree of reinforcement.

The following examples will serve to illustrate the practice of the invention in more detail. The lignin employed in these examples was a commercial material known as Indulin A. It is a purified pine wood alkali lignin derived from paper pulp sulfate black liquor. It is a brown, free-flowing amorphous powder typically having a specific gravity of 1.3, a moisture content of 4.3%, an ash content of 0.4%, an aqueous slurry pH of 3.4, a methoxyl content of 13.9%, an apparent density of 25 pounds per cubic foot, a fusion point of 250-275 C., and a sulfur content of 0.8-1.5 It is insoluble in water and aqueous acids and in non-polar solvents. It is soluble in many polar solvents and in alkaline solutions.

EXAMPLE 1 3.0 kg. of Indulin A were dissolved in 12.7 liters of water containing 3.0 kg. of sodium hydroxide. This solution was blended into 13.1 kg. of a GR-S (butadiene: styrene) type 1500 latex, having a total solids content of 23%, and in which the rubber had a Mooney viscosity of 120 ML 4. The liquids were thoroughly mixed, forming a sodium lignate-latex blend, called lignex.

The lignex was then flocculated by adding it, with rapid stirring, to 44 liters of water having a temperature of C. and containing 1.0 liter of 90% formic acid. One minute later, 1.5 kg. of a commercial hydrocarbon oil used in rubber processing, known as Sundex 53, which had previously been heated to a temperature of C., were slowly added to the rapidly stirred liquid, and high speed stirring was continued for another five minutes.

The liquid was then stirred slowly while an additional 13.1 kg. of the GR-S latex were added. Slow stirring was continued for 5 minutes after this addition.

The coprecipitate was allowed to stand for 10 minutes; then the slurry was filtered through coarse cotton filter cloth, first by gravity, and finished by suction. The filter cake was thoroughly washed by stirring it on the filter while running water over it. The cake or masterbatch was dried for 3 days in vacuo at a temperature of 80 C.

g. of the masterbatch were placed on a hot mill and masticated for 5 minutes at 300 F. The purpose of this hot milling was to remove moisture because the 'polyisocyanate might otherwise react preferentially with zbbmpounding of. the stockswass completed by addiug :the following ingredients in the amountshownz .contained 0.4 part of the Cumate accelerator, but did not differ otherwise from the'polyisocyanate-treated prepara- ,tions.

. EXAMPLE .2

A study of'various 'polyisocyanates "was made in this example. Five difierent commercial polyisocyanates were compared in the treatment of thesame oil extended GR-S/lignin masterbatch'as'used in Example 1. These polyisocyanates were:

90% diphenylmethane diisocyanate V ph nylmethane :diisocyanate Toluene diisocyanate Triphenylmethane tr'iisocyanate, in methylene dirid ,y Y 1 v "Hexamethylene 'diisocyanate f The masterbatchwas fir's't worked 5 niinutesat 300 on a hot mill for thepurpose of' dryingQhasbefore, followed by coolingandincorporatio'n ofthe polyisdcyanate on'theco'ol mill. t.

Each mixture was theri'transferred' toaihotl mill and masticated for 5 minutes more arson F. Each mixture was thereafter compounded on a cool mill according to Recipe I, supr'aQeXcept-rth'at the accelerators and sulfur were .reduced-zas :the1isocyanatewasxincreased, to attain 5 90% diphenylrnethane diisocyanate;

Table I Temperi Parts of g zg g' Modulus 'Elonga Duron MDT 1 mimn Relative at 300% Torsional Tensile t tlonlat .eter-hard- Stock per 100 afterg abrasion elongation hysteresis strength, break ness parts of adding rating (p.s.i. at 280 F. p.s.i. 7 (percent) ,(A scale) rubber DI, 7

7 .177 1, 360 0. 088 2, 680 470 v 5a 201 1,750 0.079 2,850 390 300' J=l62 v1, 220' 0. 077 2, 970 5.00 57 300 -l80 V 1, 560 0.069 2, 740 390 58 300 100 1, 000 0.126 2, 470 490 "58 1.;Room temperature.

i Control.

From the data in TableLit will be seen that the polyisocyanate treatment improved the laboratoryabrasion ;resistance by roughly 60 to when 2 parts per hundred of rubber of the MDI (9 0% diphenylmethane diiso- 'cyanate) were used, and about to when 6 parts were used. Also, the polyisocyanate treatmentsignificantly increased the modulus and decreased the torsional hysteresis.

The polyisocyanate treatment also roughly doubled "the'bou'nd rubber (indicating "an increased degree of reinforceme'nt). Thus, stocks of the kind "illustrated by fs'tocks A'and C in Table I above gave the following gel and'bound rubber values, in comparison to a control in which the stock received no diisocyanate treatment but was simply massed on a mill 'at room temperature:

. Percent Percent Stock gel bound rubber A:- :63 p 60 C 58 51 Control "46 30 proper cures in accordance with conventional compounding practice a p I I a Physical data for stocks having comparable moduli are set out in TableIIc 1 f "Tableil (1)1OOMPOUNDING AND TREATMENT I As20% solution in methylene dichloride,

The various polyisocyanates appear. to be roughly about equal in efiicacy of treatment, 'the'range of abrasion improvement being about 46 to 74%, averaging roughly 60% improvement. .In all cases there are additional benefits in reduced hysteresis, and reduction of hardness of vulcanizates. 'The above data indicate increase in modulus with decreased accelerator requirement, associated with the polyisocyanate treatment.

EXAMPLE 3 This example shows the effects of adding polyisocyanates without any hot milling. ,In this example two masterbatches were prepared.

One masterbatch (masterbatch 3A), was a single-step coprecipitate of 100 parts #1500 GR-S and 40 parts lignin. The second masterbatch (masterbatch 3B), was prepared in essentially the same manner except that 50 parts of lignin were coprecipitated. The result of physical tests of stocks made from masterbatches 3-A and 3B are set out in Tables III, A and III, B respectively.

Amounts of selected polyisocyanates (based upon dry weight of the rubber) were added to separate'portions of 140 parts each of masterbatch 3-A as shown in Table III, A and to separate portions of 150 parts each of masterbatch 3B as shown in Table HI, B.

The control and diisocyanate treated batches of Table III, A were cool milled for minutes, then compounding was completed on a cool mill.

In Table III, B a control containing parts lignin was run which was milled 12 minutes at 300 F., whereas the treated batches were milled 12 minutes on a mill at room temperature before further compounding. The purpose of this variation was for comparison of masterbatches which had been treated according to the invention and cool milled, with an untreated masterbatch which had the benefit of hot milling.

Ingredient: Parts (per hundred of rubber) Zinc oxide (Kadox) 5. Hydrocarbon oil plasticizer (Paraflux) 5. Stearic acid 2.

Benzothiazyl disulfide (MBTS) 1.5. Copper dimethyl dithiocarbamate (Cumate) 0.15 to 0.35

to achieve desired cure.

Sulfur 2.5.

Physical data of masterbatch 3-A (40 parts of lignin) are given in the following Table III, A.

Table III, A

Relative increase in abrasion resistance by-use of the polyisocyanate is about the same when all milling is cool as when it is hot; however the level of the ratings is considerably lower for the former. Over the rangeof l-8 parts of polyisocyanate per hundred of rubber, the major increase occurred with the first 2 parts. As for the other physical properties, torsional hysteresis and hardness decreased but not to the extent achieved when hot milling was employed. Also, after 1 part there was very little change by having added up to 8' parts of the polyisocyanate. The modulus (8-300) increased with the amount of polyisocyanate. The efiect. of addition of 2 parts of various diisocyanates and monoisocyanates to the masterbatch 3B without prior hot mixing was studied, with the results given in Table III, B below:

Table III, B

Rela- Modu- Tor- Elon- Duromtive lus at sional Tensile gatlon cter Chemlcal' abra- 300% hysstrength at hardsion elongatercsis (p.s.i.) break ness (A rating tlon at (perscale) (p.s.i 280 F. cent) Control, no isoeyauate (hot mixed) 1, 040 244 3, 580 600 69 90% diphenylmethane diisocyanate 113 1. 090 203 3, 570 560 71 Toluene diis'ooyan e 1, .255 3, 790 590 72 Naphthalene dilsocyanate 120 1, 110 .267 3, 640 450 71 Alpha-naphtbyl isocyanate 77 810 325 3, 360 620 81 Phenyl isocyanate 78 860 .335 3, 57 0 79 Although the treated masterbatch was not heat treated prior to incorporating the isocyanate, the improvement in abrasion rating is evident, even when compared with a hot processed control.

Also, it is immediately evident that monoisocyanates produced no benefit in physical properties. The monoisocyanate-treated stocks more nearly represent a true level for comparison with diisocyanate treated stocks which were not hot processed than does the hot processed control." A plausible explanation of the failure of the monoisocyanates is that the molecules of the mono type form bonds only with either the rubber hydrocarbon or the lignin but not with both, as are thought to take place when the polyisocyanates are added.

. Thus, it may be concluded that increase in abrasion resistance and modulus, and reduction in hysteresis and hardness, accompany polyisocyanate treatment of cold mixed stocks, though these improvements are less when compared with similar treatment of a lignin masterbatch with prior hot mixing. (See Table III, B above.)

EXAMPLE 4 In this example, a 100 part #1500 GR-S/SO parts lignin masterbatch, following the same recipe as was used previously but which was hot milled 5 min. at 300 E, was prepared for the purpose of studying the elfect of variations in accelerators on polyisocyanate treated GR-S/lignin mixtures. After addition of the polyisocyanate, the mixture was milled for an additional 10 minutes at room temperature. That portion of the masterbatch used as a control was hot milled for 12 minutes so that hot milled control stock could be compared to the polyisocyanate-treated stocks. The results are set out in Tables IV, A and IV, B (the amounts of the ingredients being expressed as parts per hundred parts of rubber).

meme

Table IV, A Bound rubber was "about doubled-by thez polyisodyanat treatment and light milling does not afieet this rade. Pfarts Relallvlodu- T Elon- Du- Swelling index measurements show a much tighter gel Treatment 8 b af, ggglg 13%" structure brought about by the polyisocyanate treatment.

tor sion elonga-(p.s.1.) break ness (A (cumrating tlon, (perscale) EXAMPLE 5 ate) p.s.1. cent) a I In this example, a large scale masterbatch of pilot gfiilf gg g g 0. 4 100 1,270 3,120 510 09 -plant size waspre'p'ared from which tire treads were made ane diisocyanate, -forlaboratory and road tests. lpart 0.3 134' 1, 000 3,130 370 04 9(l%dip l 1enylmeth- The masterbatch conslsted essentlally of GR-S/type M7 147 L930 2 900 65 1500 latex (22.3% T.S., having a Mooney viscosity of T 1 d V V n p n 0.27 127 1,770 3,380 450 71 $9? 5 f F P? i q pi 92 p 515 7 parts GR-S to 50 parts l1gn1n dry sol1ds by we1ght. Ih s These data confirm previous experience with diisomasterbatch was Pemasfimd for minutes 3.000512 .icyanate treatment. of lignin masterbatches which Show: before addition of thediisocyanate; the untreated control 1) 30 to 50% improvementin abrasion rating, was hot mlllfm for 10 mfnutes at u I w (2) Higher '*modulus and reduced accelerator require- C e y P dlphenylmethane dusocyanate ment. used for "the treatment. After the incorporationof'the Table IV, B

Parts U I -Durom- Relative Modulus at Torsional ,Tenslle Elongation eterhardu abrasion 300% elonga- 'hyst'eresls at strength at break ness J MDI1 MBTS G'umute V SulIur 3 rating tion (p.s.i.) -=280 F. (p.'s.i.) (percent) (A scale) None 1.5 0.4 2.5 100 1,290 .219 3,240 510 07 1 95% dlphenylmetbane diis ocyanato.

A For 'a steektreated with lpartur 'MDI (90% ui- "iiiisoc'yan'atfe (about 5 minutes), the masterbatchrwas phenylmethane dnsocya'nate) the best phys1cal'p1'opertles .post milled 2 min. at a stock temperature of 0 1 .19 'Q W about lff Physical test data for comparable 9111'68581'32 f(MBTS) and about the copper d1methyl'd1th1ocar- 1 "bamate (cur'nate') normally used'in an untreated stock.

This confirms previous experiments in-which theuse of Table V, A I 2 parts of diisocyanate required about /3 the benzor, A thiazyl disulfide and the"copper dimethyl dithiocar- R1 d D ba'm'ate normally used in the *untr'eatedcontrol stock y g fgg g' gg iI-he -poly1socyanate treatments resulted=1n the des1red T ia e f e a e k increase in abrasion rating 30-50% and reduction in 5. ggg 5 35 ;552 1; 2:5 5 33; 225 hysteres1s'andhardness. 1.. (p.s.1. cent) To study the lstorage'stability of theitreated master- I, i I 1 p a I v f batches, the 'geland bound rubber of-treated'raw stocks g g'ggg gggt q 1,420 2,800 62 were determined after bin storage for :1 month. Both gnercially pure unmilled and'freshly-milled "samples were tested foring ggg g figgi f dications of Setting up or formation of loosely gelled 10 0-partsoirub v ls'tructure. The results are-tabulated -in-'Tab1e IV, C. 132 1,530 m 3370 440 I 52 Table IV, C I CT? OF M ON GE AND RUBBER; The-nnprovement 1n abras1onres1stance by. the polypoly'ibcyanate Percem ,Swnmg Percent isocya'n'ate treatment :is about 30%; hysteresisand hardtreatment Treatment a gel "index boggg ness are reduced about as usual.

' ILl 1 The control stock 'anddusocyanate treated stock were m 50 27 used to recap 6.70 x 15 tires. Sets of 't'ires composed o sl t 1 l of control stock and 'diisocya'nate treated stock were Do Light mini! 68 5B 5 placed on a taxicaband on a'newspaper delivery truck in Los Angeles. "Lhbdrato'rfiahys'ibal test data. of tire 5118 55 90%"dipbenylmethane diisd'c'yanate, 'per hufidred parts or stock's'curedtor' fi min. at 4541- cures and results of tread 11 wear in use on the taxicab and delivery truck are compared in Table V, B:

- The polyisocyanate treated stockshows. about 30% improvement by the laboratory abrasion test, whereas in the wear test the treatment resulted in 30% and 22% improvement for taxicab and newspaper delivery service, respectively.

EXAMPLE 6 To show that a polyisocyanate additive to rubber/lignin mixtures is not limited to butadiene-styrene' copolymers, the following masterbatch of lignin/butadiene-vinylpyridine rubber was prepared as follows:

12 kg. (26.5 lb.) of Indulin A were suspended in 48 1. (12.7 gal.) of water at 40 to 50 C. With continuous stirring, a solution of 1.2 kg. (2.65 lb.) of sodium hydroxide dissolved in 2.5 l. (0.66 gal.) of water-was added. Stirring was continued an additional 10 minutes or until all the lignin was dissolved to form sodium lignate.

The sodium lignate solution was added slowly to 135 kg. (298 lb.) of a latex containing 30 kg. (66.1 lb.) of a 2-methyl-5-vinylpyridine:butadiene (25:75) copolymer using a mechanical stirrer to form a lignex.

A fiocculating solution consisting of 4.2 l. 1.11 gal.) of 90% formic acid diluted by addition of 460 l. (122 gal.) of water at 90 C. was prepared. To this flocculating solution under a high speed stirrer the lignex was slowly added and stirring continued minutes after final addition of the'lignex. The lignin and vinylpyridine copolymer rubber coflocculated.

The flocculated lignin-rubber composition was filtered using suction.

The lignin-rubber filtrate was then reslurried by adding water to produce a total of 250 to 300 gallons. The temperature is preferably about 70 C. Suction was continued to dry the filtrate as much as possible.

The filtrate was thereafter transferred to a circulating air oven and dried at 150 F. This batch yielded about 90 to .93 lbs. of coflocculated ligninvinylpyridine rubber containing 40 parts lignin per 100 parts dry rubber solids.

Two portions of the masterbatch were each placed on a hot mill. One portion was transferred to a cool mill at the end of 5 minutes and had added thereto on the cool mill 2 parts of 90% diphenylmethane diisocyanate (per 100 parts of rubber); it was then replaced on the hot mill and milled an additional 5 minutes at 300 F. The other portion, the control, continued milling 12 minutes on the hot mill before cooling. Both'portions were then compounded on a cool mill as follows:

control only.

12 Table VI presents data for vulcanizates made from the treated and control stocks having comparable cures;

Table VI Modu- Elon- Durom- Reln- Torlus at Tensile gation eter tive sional Treatment 300% strength at hardnbrahysterelonga- (p.s.i.) break ness (A sum esis at tion per scale) rating 280 F. (p.s.i.) cent) None (control) 1,300 2,810 600 67 100 .222 Diphenylmethane diisoeyanate 1,440 2,720 470 68 114 .234

The data show that the abrasion resistance was improved.

' EXAMPLE 7 A masterbatch was prepared consisting essentially of (:75) methyl methacrylate-butadiene 122 F. copolymer 100 parts and Indulin A lignin 50 parts, following the recipe set forth under Example 3, supra, except the methyl methacrylate-butadiene copolymer was substituted for the butadiene-styrene used in that example.

To one portion of the masterbatch were added 2 parts of 90% diphenylmethane diisocyanate. A second portion was untreated for control purposes. The procedure and recipefollowed were essentially those set out in Example 6' except added accelerators (benzothiazyl disulfide and I copper dimethyl dithiocarbamate) were added to effect a satisfactory cure. Hot milling at 300 F. for a minimum of 5 minutes after treatment appeared to enhance the physical properties of the stocks.

Selected data based upon equivalent cures are set out in Table VII.

Treatment of this masterbatch with polyisocyanate produced improvements in physical properties similar to those observed in cold GR-S/lignin mastebatches, abrasion resistance and modulus were increased and torsional hysteresis and stock hardness were reduced significantly.

Exmrus 8 Since commercially prepared GR-S #1500/1ignin is readily available in the ratio of 100 parts GR-S to 70 parts lignin under the trade name of Indulin-70-GRS, the following experiment was performed, in which such a high lignin content masterbatch was cut back by merely adding dry polymer (GR-S, type 1500), on a mill and subsequently treating it with 2 parts (per hundred of rubber) of diphenylmethane diisocyanate procured from Du Pont, as a further embodiment of this invention.

The masterbatch was milled at 300 F. After 10 minutes a portion was transferred to a cool mill, had added thereto 2 parts of the diisocyanate, and was then transferred back to the hot mill where it was milled 5 minutes more. The remaining portion of the masterbatch (the control) was allowed to remain at 300 F. on the hot mill 12 min. before cooling; the control was not remilled as was the treated stock.

Both portions were compounded as in Example 7 above with minor variations in the accelerators to obtain proper cures.

Data gathered from tests of stocks made therefrom are presented in Table VIII. Comparison of treated stock to untreated control stock is made in Table VIII.

estate Selected data of cures having'compa-r al'lle values are set forth below:

It may be seen that'though the lowredhy steresis and reduced" hardness; compare favorably with a regularly prepared coprecipitate 'of 40 or 50 partslig'nin as set out in Examples 1 through '4, supra, the abrasion resistance improvement is less pronounced though appreciable.

V I v EXAMPLE 9 w i A lignex cofiiprised of'I'OO or Hevea rubber latex and 50 parts (per hundred of rubberlof ligni'n culated with'dilute formic acid to yield a master-batch.

To demonstrate the invention, a "first portion of the masterbatch, designated A, was milled for 5 minutes at 300 vF., after which 2 parts (per hundred ofrubber) of v rcdi stilled :toluene 'diisocyanate were incorporated in the maste'rba tch by mixing for 5 minutes on a coolLmill.

The stock was then milled for an additional 5 minutes at As a control, a second portion of the masterbatch, designated B, was milled for 12 minutes at 300 F.

The diisocyanate-treated portion A and the control portion B were then compounded with vulcanizing ingredients on a cool mill, in essentially the same manner as in previous examples. After curing samples of these stocks in a press at 45 p.s.i. steam pressure for varying times, the physical properties were as shown in Table IX.

Table IX Diisocyanate treated Untreated control stock A stock B Time of cur 22 45 90' 22 45 90 Test:

Modulus at 300% elongation (p.s.l.). 1, 900 1, 960 1, 700 1, 870 1, 660 1, 400 Tensile strength (p.s.1.) 3, 100 2, 770 2, 350 3, 110 3, 040 2, 840 Elongation at break (percent) 430 420 360 440 460 570 Durometer hardness (A scale) 55 55 56 63 64 64 Torsional hysteresis at 280 F .091 .076 169 174 Relative abrasion rating 116.1 104.1 84. 2 70. 2

These data show the improvement in abrasion resistance, lowered hysteresis, and decreased hardness resulting from the polyisocyanate treatment of the invention.

In view of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection afiorded the invention.

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

1. The method which comprises incorporating an organic polyisocyanate in a dry lignin-rubber co-coagulum of a mixture of a rubber latex and an alkaline aqueous solution of lignin, the lignin being in quantity not more than 100 parts per 100 parts of rubber in the ligninrubber co-coagul-um, and the polyisocyanate being in quantity not more than parts per 100 parts of said rubber, said rubberbeingselectd froi'n' -the gi'oiipcorisi mg of natural rubberandsynthetic rubber 'polymers of material selected from the group consisting of buta' bi es-1,3 and mixturesof butadinesdfl withfcompounds contain a CH C group and are copolymer izame with butadieneS-LS. I I

The method which comprises incorporating a'ri 'drgarlic polyisocyanate in a Iignin r'ubber co coagiilum of a mixture of a rubber latex and an "alkaline aqueous solution of lignin, the lignin being in amount from-25 to parts per 100 parts of rubber in the-lignin-rubbei' eo-coagulum, and the polyisocyanate being in amount from 0.5 to 10 parts per ;100 parts of said 'rubberfsaid rubber being selected from the group-consisting of hatu'ral rubber and synthetic rubber puymersermaterial se lected from the group consistingof butadiehes-L3 and mixtures of butadienes-LS with-compoundswhich con- 'tain a'CH =C group and are copolyrneri'zable with butadienes-1,3. v I

3. The method which comprises heating at a temperature from 200 'F. to 350 F. for 5 minutes to 10 'hours a dry lignin-rubber'co-coagulum of a 'mixture'of a rubber latex and an alkaline aqueous sem n of lignin, the ratio-of lignin to rubber in the oo-coagu'lilrn being 25 to 100 parts of lignin per 100 parts of'riibber, and

-thereafter"mixing into the thus treated lignin-rubber 'coag'ulum 0.5 to 10 'parts'bf organic polyisocyanate ;per' 1'0'0 parts 'of said rubber, said rubber being selected from the group consisting'of natural rubber and syntlitic' rubber polymers of inaterial selected *rrtim' the group consisting of butadienes-1,3 and mixtures of butadienes-1,3 with compounds which contain a CH C group and are copolymerizable with butadienes-1,3.

4. The method which comprises heating for 2 to 30 minutes at a temperature from 200 F. to 350 F. a mixture of an organic polyisocyanate and a dry ligninrubber co-coagulum of a mixture of a rubber latex and an alkaline aqueous solution of lignin, the lignin being in amount from 25 to 100 parts per 100 parts of rubber in the lignin-rubber co-coagulum, and the polyisocyanate being in amount from 0.5 to 10 parts per 100 parts of said rubber, said rubber being selected from the group consisting of natural rubber and synthetic rubber polymers of material selected from the group consisting of butadienes-l,3 and mixtures of butadienes-1,3 with compounds which contain a CH ==C group and are copolymerizable with butadienes-1,3.

5. The method which comprises heating at a temperature from 200 F. to 350 F. for 5 minutes to 10 hours a dry lignin-rubber co-coagulurn of a mixture of a rubber latex and an alkaline aqueous solution of lignin, the ratio of lignin to rubber in the co-coagulum being 25 to 100 parts of lignin'per 100 parts of rubber, thereafter mixing into the thus treated lignin-rubber cocoagulum 0.5 to 10 parts of an organic polyisocyanate per 100 parts of said rubber, and thereafter heating the mixture of polyisocyanate and lignin-rubber co-coagu lum for 2 to 30 minutes at a temperature from 200 F. to 350 F., said rubber being selected from the group consisting of natural rubber and synthetic rubber polymers of material selected fromthe group consisting of butadienes-1,3 and mixtures of butadienes-1,3 with compounds which contain a CH =C group and are copolymerizable with butadienes-1,3.

6. The method of claim 2 in which the polyisocyanate is diphenylmethane diisocyanate.

7. The method of claim 2 in which th polyisocyanate is toluene diisocyanate.

8. The method of claim 2 in which the polyisocyanate is triphenylmethane triisocyanate.

9. The method of claim 2 in which the polyisocyanate is hexamethylene diisocyanate.

10. The method of claim 2 in which the polyisocyanate is naphthalene diisocyanate.

11. A rubber stock comprising 100 parts of a rubber,

from 25 to 100 parts of lignin, and from. 0.5 to 10 parts of an organic polyisocyanate, said rubber and lignin having been co-coagulated from a mixture of rubber latex and an alkaline aqueous solution of lignin, and said polyisocyanate having been mixed into the dry lignin-rubber co-coagulum, said rubber being selected from the group consisting of natural rubber and synthetic rubber polymers of material selected from the group consisting of butadienes-1,3 and mixtures of butadienes-lfl with compounds which contain a CH =C group and are copolymerizable with butadienes-l,3.

12. A rubber stock as in claim 11 in which the polyisocyanate is diphenylmethane diisocyanate.

13. A rubber stock as in claim 11 in which the po'lyisocyanate is toluene diisocyanate.

14. A rubber stock as in claim 11 in which the polyisocyanate is triphenylmethane triisocyanate.

15. A rubber stock as in claim 11 in which the polyisocyanate is hexamethylene diisocyanate.

16. A rubber stock as in claim 11 in which the polyisocyanate is naphthalene diisocyanate.

17. A product comprising a vulcanized rubber composition comprising 100 parts of a rubber, from 25 to 100 parts of lignin, and from 0.5 to 10 parts of an organic polyisocyanate, said rubber and lignin having been cocoagulated from a mixture of rubber latex and an. alkaline aqueous solutionof lignin, and said polyisocyanate having been mixed into the dry lignin-rubber co-coagulum, said rubber being selected from the group consisting of natural rubber and synthetic rubber polymers of ma- "1-6 .terial selected from the group consisting of butadienes- 1,3 and mixtures of butadienes.-1,3 with compounds which contain a CH C group and are copolymerizable' with butadienes-1,3.

18. A rubber stock comprising a .rubber and lignin and organic polyisocyanate, the being in quantity not more than parts per 100 parts of a rubber, and the polyisocyanate being in quantity not more than 10 parts per 100 parts per 100 parts of a rubber, said rubber and lignin having been co-coagulated from a mixture of a rubber latex and an alkaline aqueous solution of lignin, and said polyisocyanate having been mixed into the dry lignin-nubb'er co-coagulum, said rubber being selected from the group consisting of natural rubber and synthetic rubber polymers of material selected from the group consisting of butadienes-1,3 and mixtures of butadienes- 1,3 with compounds which contain a CH C group and are copolymerizable with butadienes-l,3.

References Cited in the file of this patent UNITED STATES PATENTS Neal et a1. Feb. 17, 1948 Pollak Aug. 26, 1952 OTHER REFERENCES relied on. 

1. THE METHOD WHICH COMPRISES INCORPORATING AN ORGANIC POLYISOCYANATE IN A DRY LINGIN-RUBBER CO-COAGULUM OF A MIXTURE OF A RUBBER LATEX AND AN ALKALINE AQUEOUS SOLUTION OF LIGNIN, THE LIGNIN BEING IN QUYANTITY NOT MORE THAN 100 PARTS PER 100 PARTS OF RUBBER IN THE LIGNIN RUBBER CO-COAGULUM, AND THE POLYISOCYANATE BEING IN QUANTITY NOT MORE THAN 10 PARTS PER 100 PARTS OF SAID RUBBER, SAID RUBBER BEING SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER AND SYNTHETIC RUBBER POLYMERS OF MATERIAL SELECTED FROM THE GROUP CONSISTING OF BUTADIENES-1,3 AND MIXTURES OF BUTASDIENES-1,3 WITH COMPOUNDS WHICH CONTAIN A CH2=C< GROUP AND ARE COPOLYMERIZABLE WITH BUTADIENES-1,3. 